The present invention relates to a variable displacement swash plate compressor.
Japanese Laid-Open Patent Publication No. 5-172052 discloses a variable displacement swash plate compressor (hereinafter referred to as compressor). The compressor includes a housing formed by a front housing segment, a cylinder block, and a rear housing segment. The front housing segment includes a first suction chamber and a first discharge chamber. The rear housing segment includes a second suction chamber and a second discharge chamber. The rear housing includes a pressure adjustment chamber.
The cylinder block includes a swash plate chamber and cylinder bores. Each cylinder bore includes a first cylinder bore, which is formed in the front side of the cylinder block, and a second cylinder bore, which is formed in the rear side of the cylinder block. A radial bearing is arranged near the first cylinder bores of the cylinder block. A control pressure chamber, which is connected to the pressure adjustment chamber, is formed near the second cylinder bores of the cylinder block.
A drive shaft, which extends through the housing, is rotatably supported by radial bearings in the cylinder block. A swash plate, which is rotated by the drive shaft, is arranged in the swash plate chamber. A link mechanism is located between the drive shaft and the swash plate to change the inclination angle of the swash plate. The inclination angle refers to the angle of the swash plate relative to a direction that is orthogonal to the rotation axis of the drive shaft. Each cylinder bore receives a piston, which is reciprocated in the cylinder bore to form a compression chamber. When the swash plate rotates, a conversion mechanism reciprocates the piston in each cylinder bore with a stroke that is in accordance with the inclination angle. An actuator changes the inclination angle of the actuator, and a control mechanism controls the actuator.
The actuator, which is arranged in the control pressure chamber, is not allowed to rotate integrally with the drive shaft. More specifically, the actuator includes a non-rotation movable body that covers a rear end of the drive shaft. An inner surface of the non-rotation movable body supports the rear end of the drive shaft so that the drive shaft is rotatable relative to the non-rotation movable body and movable in the axial direction. An outer surface of the non-rotation movable body is movable in the axial direction in the control pressure chamber but not about the rotation axis. A pushing spring is arranged in the control pressure chamber to urge the non-rotation movable body toward the front. The actuator includes a movable body that is coupled to the swash plate and movable in the axial direction. A thrust bearing is arranged between the non-rotation movable body and the movable body. A pressure control valve is arranged between the pressure adjustment chamber and the discharge chamber to change the pressure in the control pressure chamber and move the non-rotation movable body and the movable body in the axial direction.
The link mechanism includes a movable body and a lug arm, which is fixed to the drive shaft. The rear end of the lug arm includes an elongated hole that extends toward the rotation axis from the outer side in a direction orthogonal to the rotation axis. A pin is inserted into the elongated hole to support the front side of the swash plate so that the front side is tiltable about a first tilt axis. The front end of the movable body includes an elongated hole that extends toward the rotation axis from the outer side in a direction orthogonal to the rotation axis. A pin is inserted into the elongated hole to support the rear side of the swash plate so that the rear side is tiltable about a second tilt axis, which is parallel to the first tilt axis.
In the compressor, the pressure adjustment valve is controlled to open and connect the discharge chamber and the pressure adjustment chamber so that the pressure of the control pressure chamber becomes higher than the pressure of the swash plate chamber. This moves the non-rotation movable body and the movable body forward. As a result, the inclination angle of the swash plate increases, and the stroke of the pistons increases. The compressor displacement of the compressor for each drive shaft rotation also increases. When the pressure adjustment valve is controlled to close and disconnect the discharge chamber and the pressure adjustment chamber, the pressure of the control pressure chamber decreases to the same level as the pressure in the swash plate chamber. This moves the non-rotation movable body and the movable body rearward. As a result, the inclination angle of the swash plate decreases, and the stroke of the pistons decreases. The compressor displacement of the compressor for each drive shaft rotation also decreases.
In a compressor like the one described above, compression reaction force, discharge reaction force, and the like that act on the pistons produce a radial load that acts on the drive shaft. Thus, even though the radial bearings are arranged between the housing and the drive shaft, displacement of the drive shaft in the radial direction is unavoidable. This tendency is especially outstanding in the compressor described above because there is no radial bearing in the proximity of the first cylinder bores. In such a compressor, when the actuator moves, the non-rotation movable body moves in the axial direction relative to the drive shaft inside the control pressure chamber.
In the above compressor, an O-ring is arranged between the outer surface of the non-rotation movable body and the inner surface of the control pressure chamber. When the actuator moves in the compressor, the radial load produced by the drive shaft may deform the O-load beyond a tolerable margin. In this case, the outer surface of the non-rotation movable body may interfere with the inner surface of the control pressure chamber, and a friction force proportional to the radial load would act between the outer surface of the non-rotation movable body and the inner surface of the control pressure chamber. This would hinder forward and rearward movement of the non-rotation movable body and the movable body in the compressor. Thus, the controllability would be low when varying the compressor displacement.
In particular, when increasing the inclination angle of the swash plate to increase the compressor displacement, the radial load acting on the drive shaft increases. This increases the friction force. Thus, the time used to increase the compressor displacement would become longer. This would affect the response of the compressor and cause a cooling delay. In order to avoid such a situation, the control pressure chamber would have to be enlarged in the radial direction so that the non-rotation movable body and the movable body overcome the friction force when moving forward. However, this would enlarge the housing and consequently the compressor. Thus, limitations may be imposed on the arrangement of the compressor when installing the compressor in a vehicle or the like.
When enlarging the control pressure chamber in the radial direction to increase the compressor displacement, the volume of the control pressure chamber increases, and a longer time would be used to decrease the pressure of the control pressure chamber. In this case, the compressor displacement cannot be readily decreased when the vehicle is accelerated. Further, if there is a delay in the decrease of the compression when the engine speed is low and the compressor displacement remains high, the control executed by an ECU may stall the engine. If the engine were to be controlled in accordance with such slow changes in the compressor displacement, the control executed by the ECU would be complicated.